Monitoring MySQL with DTrace/SystemTap

SystemTap/DTrace with MySQL & Drizzle Padraig O'Sullivan Software Engineer, Akiban Tech. posullivan@akiban.com http://posulliv.github.com/ These slides released under the Creative Commons AttributionNoncommercialShare Alike 3.0 License

About Padraig  Software Engineer at Akiban Technologies in Boston  Drizzle contributor for over a year now  Ported the DTrace probes from MySQL to Drizzle...hence this talk!  Actually going to spend most of this talk discussing SystemTap since I'm assuming everyone is familiar with DTrace

What is DTrace?  Observability technology that allows the behaviour of systems and applications to be investigated easily  Developed at Sun and runs on Solaris and OSX  Zero probe effect when not enabled and system acts as if DTrace not present at all  Has a scripting language called “D”  It doesn't work on Linux currently

What is SystemTap?  Project under development since 2005 for dynamic instrumentation of Linux systems − Contributions come from Red Hat, IBM, Oracle, etc.  SystemTap can accomplish the same tasks as DTrace  Static DTrace probes in an application can be used with SystemTap − Latest version comes with python script named dtrace for this  Has production support since RHEL 5.4

How SystemTap Works  SystemTap has a command-line interface named stap − Takes script in C-like language  Basic steps Systemtap performs are: − Translates the .stp script into C source code − Compiles the C code into a kernel module (.ko file) − Loads the module into the kernel − Module runs − Module is unloaded when CTRL-C is given or module decides it is done

How SystemTap Works Probe script & Debug info Translate (Parse, elaborate And translate) Generated C file Build Generated Kernel module Plugin Load and Probe output Registration execute Unload

Probes  Essential idea behind a SystemTap script is to name “events” and give them “handlers”  When a specified event occurs, the kernel runs the handler and then resumes execution  Combination of an event and a handler is referred to as a probe in SystemTap

Simple Example – syscall probing # stap -e 'probe syscall.open > { > log(execname() . “: “ . filename) > }' bash: / bash: /tmp cat: /etc/ld.so.cache cat: /tmp/padraig sendmail: /proc/loadavg cat: <unknown> ...

iotop in SystemTap global reads, writes, total_io probe vfs.read { reads[execname()] += $count } probe vfs.write { writes[execname()] += $count } # print top 10 IO processes every 5 seconds probe timer.s(5) { foreach (name in writes) total_io[name] += writes[name] foreach (name in reads) total_io[name] += reads[name] printf ("%16st%10st%10sn", "Process", "KB Read", "KB Written") foreach (name in total_io- limit 10) printf("%16st%10dt%10dn", name, reads[name]/1024, writes[name]/1024) delete reads delete writes delete total_io print("n") }

iotop in SystemTap # stap iotop.sty Process KB Read KB Written firefox 3200 0 Gnome-terminal 3060 0 mysql 528 22 mysqld 23 63 hald-addon-inpu 14 0 gnome-power-man 12 0 #

Getting SystemTap  Recommend going with Fedora 11/12 or RHEL if you want to use SystemTap easily. What's needed: − systemtap − systemtap-sdt-devel − systemtap-runtime − Kernel debuginfo  Quite stable on these platforms and usually works just as advertised

SystemTap on Ubuntu/Debian  This is not as easy! What's needed: − systemtap − systemtap-sdt-dev − A kernel compiled with debug information − A kernel that supports utrace if you want to perform user level probing  In order to perform user-level probing, you will need to compile/install a custom kernel that supports utrace

Dtrace/SystemTap Comparison  Obviously there is the licensing difference but we won't discuss that here  Both tools are said to be safe to use in production  DTrace comes by default in Solaris. Not so with SystemTap on Linux distributions  From a user's perspective, SystemTap can be a pain to get working (particularly on Ubuntu/Debian)  DTrace just works straight out of the box

MySQL & Drizzle with SystemTap  Symbolic probing in which function names can be used for probes: − Relies on knowledge of the source code of the application  Instrument the application with marks − Only requires us to know what the markers for the application are  Luckily, MySQL and Drizzle have static Dtrace probes which correspond to the second method listed above

MySQL & Drizzle with SystemTap  MySQL comes with static DTrace probes − I ported these probes to drizzle  SystemTap is compatible with static DTrace probes − Any probe we define in our application for Dtrace can be used by SystemTap also  In order to build MySQL and Drizzle with SystemTap support the systemtap-sdt-dev package needs to be installed

MySQL & Drizzle with SystemTap  To build MySQL and Drizzle for use with SystemTap, it's pretty straightforward: Drizzle $ ./config/autorun.sh $ ./configure –with-debug –enable-dtrace $ make MySQL $ ./BUILD/autorun.sh $ ./configure –with-debug –enable-dtrace $ make

Static Probes in MySQL & Drizzle  Once MySQL/Drizzle is configured and built and we start the server, we can list the markers that are present in the server: # stap -l 'process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("*")' process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("net__write__start") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("net__write__done") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("net__read__start") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("net__read__done") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("connection__done") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("connection__start") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("query__parse__start") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("query__parse__done") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("update__start") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("update__done") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("multi__update__start") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("multi__update__done") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("insert__start") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("insert__done") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("insert__select__start") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("insert__select__done") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("delete__start") process("/home/posulliv/repos/mysql/uc/sql/mysqld").mark("delete__done") ...

MySQL & Drizzle Static Probes  Approximately 60 probes, 200 locations in MySQL  Query cache (not in drizzle)  MyISAM key cache (not in drizzle)  Network I/O  Query execution  Drizzle has started inserting probes to the optimizer  Zero overhead when probes disabled − Overhead can get high if lots of probes firing

Measuring Time in Storage Engine global query_times global engine_times global queries probe process(@1).mark("query__start") { query_times[tid()] = gettimeofday_us() engine_times[tid()] = 0 queries[tid()] = user_string($arg1) } probe process(@1).mark("*row__start") { engine_times[tid()] = gettimeofday_us() } probe process(@1).mark("*row__done") { engine_times[tid()] = gettimeofday_us() - engine_times[tid()] } probe process(@1).mark("query__done") { query_times[tid()] = gettimeofday_us() - query_times[tid()] printf("%sn", queries[tid()]) printf("Total: %dus Engine: %dusn", query_times[tid()], engine_times[tid()]) }

Measuring Time in Storage Engine # stap se_time.sty /home/posulliv/repos/mysql/mysql-5.5.2-m2/5.5.2/libexec/mysqld select @@version_comment limit 1 Total: 1395us Engine: 0us select USER() Total: 228us Engine: 0us SELECT DATABASE() Total: 586us Engine: 0us show databases Total: 753us Engine: 5us show tables Total: 893us Engine: 5us show tables Total: 3545us Engine: 18us select * from tables Total: 22756us Engine: 5us ^C #

CPU Cycles in Storage Engine global query_times global engine_times global queries probe process(@1).mark("query__start") { # get_cycles() returns the processor cycle counter value query_times[tid()] = get_cycles() engine_times[tid()] = 0 queries[tid()] = user_string($arg1) } probe process(@1).mark("*row__start") { engine_times[tid()] = get_cycles() } probe process(@1).mark("*row__done") { engine_times[tid()] = get_cycles() - engine_times[tid()] } probe process(@1).mark("query__done") { query_times[tid()] = get_cycles() - query_times[tid()] printf("%sn", queries[tid()]) printf("Total: %d Engine: %dn", query_times[tid()], engine_times[tid()]) }

CPU Cycles in Storage Engine # stap se_cycles.sty /home/posulliv/repos/mysql/mysql-5.5.2-m2/5.5.2/libexec/mysqld select @@version_comment limit 1 Total: 370496 Engine: 0 select USER() Total: 117047 Engine: 0 SELECT DATABASE() Total: 659163 Engine: 0 show databases Total: 1189115 Engine: 8348 show tables Total: 353008 Engine: 8390 show tables Total: 2659210 Engine: 31185 insert into t1 values (2, 'sarah') Total: 8745185 Engine: 6257979 select * from t1 Total: 17086400 Engine: 9733 select b from t1 where a = 2 Total: 20495092 Engine: 61660 ^C #

Query Tracing – Lock & Filesort global lock_times global filesort_times probe process(@1).mark(“*lock__start”) { lock_times[tid()] = gettimeofday_us() } probe process(@1).mark("*lock__done") { lock_times[tid()] = gettimeofday_us() - lock_times[tid()] } probe process(@1).mark("filesort__start") { filesort_times[tid()] = gettimeofday_us() } probe process(@1).mark("filesort__done") { filesort_times[tid()] = gettimeofday_us() - filesort_times[tid()] }

Putting It All Together # stap query_trace.sty /home/posulliv/repos/mysql/mysql-5.5.2-m2/5.5.2/libexec/mysqld select @@version_comment limit 1 Total: 287us Locks: 0us Engine: 0us Network: 6us Filesort: 0us select USER() Total: 127us Locks: 0us Engine: 0us Network: 6us Filesort: 0us SELECT DATABASE() Total: 562us Locks: 0us Engine: 0us Network: 21us Filesort: 0us show databases Total: 642us Locks: 0us Engine: 5us Network: 6us Filesort: 0us show tables Total: 1148us Locks: 0us Engine: 6us Network: 6us Filesort: 0us show tables Total: 6201us Locks: 0us Engine: 19us Network: 23us Filesort: 0us SELECT DATABASE() Total: 564us Locks: 0us Engine: 0us Network: 21us Filesort: 0us show databases Total: 81us Locks: 0us Engine: 5us Network: 6us Filesort: 0us show tables Total: 293us Locks: 0us Engine: 5us Network: 6us Filesort: 0us select * from t1 Total: 1202us Locks: 32us Engine: 20us Network: 23us Filesort: 0us select * from t1 where a = 1 Total: 1134us Locks: 30us Engine: 56us Network: 21us Filesort: 0us select * from t1 order by a desc Total: 4727us Locks: 26us Engine: 20us Network: 22us Filesort: 3182us insert into t1 values (3, 'tomas') Total: 3406us Locks: 146us Engine: 858us Network: 30us Filesort: 0us select * from t1 order by a desc Total: 1340us Locks: 27us Engine: 20us Network: 21us Filesort: 228us ^C #

Hot Tables - Reads global tables probe process(@1).mark("*read__row__start") { tables[user_string($arg1), user_string($arg2)]++ } probe end { foreach ([schema, table] in tables) { printf("%s.%s %dn", schema, table, tables[schema, table]) } } # stap hot_reads.sty /home/posulliv/repos/mysql/mysql-5.5.2-m2/5.5.2/libexec/mysqld information_schema./opt/mysql_sandboxes/stap/tmp/#sql_1ecd_0 6 test.t1 8 ^C #

Hot Tables - Updates global tables probe process(@1).mark("update__row__start"), process(@1).mark("insert__row__start"), process(@1).mark("delete__row__start") { tables[user_string($arg1), user_string($arg2)]++ } probe end { foreach ([schema, table] in tables) { printf("%s.%s %dn", schema, table, tables[schema, table]) } } # stap hot_updates.sty /home/posulliv/repos/mysql/mysql-5.5.2-m2/5.5.2/libexec/mysqld information_schema./opt/mysql_sandboxes/stap/tmp/#sql_901_0 4 test.t1 3 test.t2 100 ^C #

Queries Accessing Particular Table global schema_name global table_name global queries global used probe begin { schema_name = @1 table_name = @2 } probe process(@3).mark("query__exec__start") { queries[tid()] = user_string($arg1) used[tid()] = 0 } probe process(@3).mark("*lock__start") { if (schema_name == user_string($arg1) && table_name == user_string($arg2)) { used[tid()] = 1 } } probe process(@3).mark("query__exec__done") { if (used[tid()]) { printf("%s;n", queries[tid()]) } }

Queries Accessing Particular Table # stap par_table.sty test t1 /home/posulliv/repos/mysql/mysql-5.5.2- m2/5.5.2/libexec/mysqld select * from t1; insert into t1 values (4, 'gearoid'); insert into t1 values (5, 'domhnall'); select * from t1 order by a desc; ^C #

Timing Locks global rdlocks global wrlocks probe process(@1).mark("handler__rdlock__start") { rdlocks[tid()] = get_cycles() printf("Start: Lock->Read %s.%sn", user_string($arg1), user_string($arg2)) } probe process(@1).mark("handler__rdlock__done") { printf("End: Lock->Read %d cyclesn", get_cycles() - rdlocks[tid()]) } probe process(@1).mark("handler__wrlock__start") { wrlocks[tid()] = get_cycles() printf("Start: Lock->Write %s.%sn", user_string($arg1), user_string($arg2)) } probe process(@1).mark("handler__wrlock__done") { printf("End: Lock->Write %d cyclesn", get_cycles() - wrlocks[tid()]) }

Timing Locks # stap locktime.stp /home/posulliv/repos/mysql/mysql-5.5.2-m2/5.5.2/libexec/mysqld Start: Lock->Read test.t1 End: Lock->Read 418788 cycles Start: Lock->Read test.t1 End: Lock->Read 173971 cycles Start: Lock->Write test.t1 End: Lock->Write 402910 cycles Start: Lock->Write test.t1 End: Lock->Write 704391 cycles Start: Lock->Read test.t1 End: Lock->Read 171652 cycles Start: Lock->Read test.t1 End: Lock->Read 251286 cycles ^C #

Resources and Thank You!  SystemTap wiki − Lots of documentation and tutorials on how to get started with stap  SystemTap examples − http://sourceware.org/systemtap/examples/  My blog has some articles on how to get SystemTap up and running on Ubuntu and how to configure MySQL/Drizzle for SystemTap  SystemTap script repository − http://github.com/posulliv/stap

Monitoring MySQL with DTrace/SystemTap

by Padraig O'Sullivan on Jun 28, 2010

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Monitoring MySQL with DTrace/SystemTap — Presentation Transcript